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A time-variability study of the neutral iron line flux at 6.40keV in the SgrB2 region from data of Suzaku and Chandra is presented. The highly ionized ironline at 6.68keV is due to Galactic Center Diffuse X-rays (GCDX), and is thustime invariable. By comparing the 6.68keV and 6.40keV line fluxes, we foundthat the 6.40keV flux from the SgrB2 complex region is time variable;particularly the giant molecular cloud M0.66-0.02, known as ``Sgr B2 cloud'' ishighly variable. The variability of the 6.40keV line in intensity and spatialdistribution strongly supports the scenario that the molecular clouds in theSgrB2 region are X-ray Reflection Nebulae irradiated by the Galactic Center(GC) black hole Sgr A*.

A Time-Variable X-Ray Echo: Indications of a Past Flare of the Galactic-Center Black Hole